The official language of San Marino is standard Italian, but there’s also a distinct dialect called Sammarinese. I’ve seen it referred to as it’s own language, a variation of Romagnol, and as a seperate dialect – this seems to be both because of San Marino’s sovereignty and the difficulty in drawing a line between dialects and different languages (especially in Italy). That being said, Sammarinese is considered an endangered language, as it’s increasingly not being passed on to younger generations.
Italian dialects can be very distinct from standard Italian to the point that some are really considered their own languages – there’s not a lot of mutual intelligibility between say, Lombard and Sicilian. Here’s a good look at Italian dialects as a whole:
As for Sammarinese, most sources I found describe it as a type of Romagnol, though one of the best studies on Sammarinese describes it as a “borderline Romagnol variety”, adding:
However, the findings also reveal a language that stands apart from neighboring varieties due to complex historical and geographical factors, including a Celtic substratum from the pre-Roman and Roman times, a Byzantine Greek heritage and Lombard/ Germanic influence from the second half of the first millennium, and a geographic position that resulted in linguistic isolation from the vernaculars spoken in the Central Romagnol plain.Simona Montanari, “Sammarinese, the Endangered Language of the Republic of San Marino: A Preliminary Study of Documentation and Description“
There’s not a lot of comparative examples of Sammarinese that I could find, but the Flag and Anthem Guy on Youtube is from San Marino and gives a little sample of the language: